Targeting embryonic stem cells.

Gene targeting of mouse embryonic stem cells facilitates the deliberate engineering of the mouse genome. The gene targeting vector is introduced into cells by electroporation, and cell clones carrying the targeting vector are obtained by drug selection. Clones can be screened effectively for correct recombination events by either Southern blot analysis with external and internal probes, or by long-range PCR. Positive clones are subsequently expanded and prepared for the generation of chimeric mice.